Fluoroelastomer compositions, their preparation, and their use

ABSTRACT

A curable fluoroclastomer composition comprising at least one fluoroelastomer, a bisphenol curative, and a peroxide curative provides a non-post cure flurorelastomer material suitable for use in the manufacture of, for example. When cured (vulcanized), the composition exhibits an improved compression set resistance, in comparison to the fluoroelastomer cured by the bisphenol curative alone, without performing a post-cure procedure.

[0001] This application claims benefit of U.S. Provisional ApplicationSerial No. 60/398,713, filed Jul. 29, 2002, U.S. Provisional ApplicationSerial No. 60/412,557, filed Sep. 23, 2002, and U.S. ProvisionalApplication Serial No. 60/447,290, filed Feb. 14, 2003, the entiredisclosures of which are hereby incorporated by reference

FIELD OF THE INVENTION

[0002] The invention relates to curable and cured fluoroelastomers andmolded products made therefrom, particularly sealing elements such asgaskets used in the automotive industry.

BACKGROUND OF THE INVENTION

[0003] Reducing the emissions of pollutants caused by the operation ofinternal combustion engines is a continuing goal of industry in general,and the automotive industry in particular. Developments in this areahave been spurred on in part by federal and state legislations which setlimits for the permissible levels of numerous gasses and otherpollutants that result from internal combustion engines such as thegasoline burning engines used in automobiles. For example, California'sAir Resources Board (ARB) adopted Low-Emission Vehicle (LEV) regulationsin 1990. This set of regulations requires significant reductions inautomobile emissions and run from 1994 to 2003. The ARB has sinceamended these regulations to impose even greater emission reductionrequirements. These new regulations, LEV-II, will run from 2004 through2010. LEV and LEV-II impose very stringent requirements on emissionsfrom automobiles. Other relevant regulations are the U.S. EnvironmentalProtection Agency National Low Emissions Vehicle (NLEV) standards. As aresult, the automotive industry is continuously investigating ways toreduce emissions in order to comply with these and other legislativerequirements.

[0004] Emissions from internal combustion engines include not only theresultant combustion gases, such as carbon monoxide, but also fuelemissions, e.g., the leakage of fuel vapors as the fuel, e.g., gasoline,is transported from the storage vessel to the point of combustion. Toreduce such emissions, gaskets and other sealing elements are used toseal joints. Such sealing elements are made from a variety of materialsincluding polymers, fiber composites, graphite, and steel. Typicalpolymeric gasket materials used in automobiles include silicone rubbers,fluorosilicone rubbers, and HNBR rubber (hydrogenatedacrylonitrile-butadiene rubber or hydrogenated nitrile rubber).

[0005] However, due to the demand for even lower emission levels,polymeric materials that exhibit even lower permeability to fuel vaporsare being used, for example, fluoroelastomers (FKM). Typical examples offluoroelastomers are copolymers of vinylidene fluoride andhexafluoropropylene and terpolymers of vinylidene fluoride,hexafluoropropylene and tetrafluoroethylene. These fluoroelastomerspossess not only low fuel permeability, but also excellent heatstability, good resistance to solvents, oils, and other chemicals, lowcompression set, and good processability. However, fluoroelastomers arerelatively expensive materials, and thus there is a need to reduce costsassociated with the manufacture of molded articles such as gaskets fromfluoroelastomers.

[0006] In the manufacture of molded articles from fluoroelastomers, atwo step curing or vulcanization process is typically used. First, thearticled is molded and undergoes an initial “within the mold” cureinduced by the application of heat and pressure. Subsequently, themolded article undergoes a post cure step wherein the article is heatedto, for example, 225° C.-250° C. and held at that temperature for aperiod of time, e.g., from about 12 up to 16 hours, or even up to 24hours, sometimes even up to 48 hours .

[0007] This post-cure procedure greater increases production time andcosts. For this reason, the industry has sought curable fluoroelastomercompositions that exhibit low-post cure. One such material is TechnoflonFOR HS® sold by Ausimont USA, which is said to provide a 75% reductionin post cure rate. This material is a 66% fluorine fluorocarbonelastomer combined with a bisphenol curative. In this material,hygroscopic end groups are eliminated in the polymer backbone whichresults in improved compression set because the ionic forces of the endgroups, which tend to adversely affect compression set, are mitigated.While this material does exhibit shorter post cure times, there is stilla need for materials with even lower post cure times, more particularlythere is a need for materials that can be characterized as non-post curematerials.

SUMMARY OF THE INVENTION

[0008] Accordingly, an aim of the invention is to provide a curablefluoroelastomer composition containing a cure system that results in areduced post cure time. Preferably, the inventive fluoroelastomercomposition does not require any post cure procedure.

[0009] Upon further study of the specification and appended claims,further advantages of this invention will become apparent to thoseskilled in the art.

[0010] In accordance with the invention there is provided a curablefluoroelastomer composition comprising at least one fluoroelastomer, abisphenol curative, and a peroxide curative, wherein when cured(vulcanized) the material exhibits an improved compression setresistance, in comparison to the fluoroelastomer cured by the bisphenolcurative alone, without performing a post-cure procedure.

[0011] In accordance with another aspect of the invention there isprovided a curable fluoroelastomer composition comprising at least onefluoroelastomer, a bisphenol curative, and a peroxide curative, whereinduring curing the bisphenol curative provides an initial cross-linkingand thereafter the peroxide curative deactivates the bisphenol curativeand provides a secondary cross-linking. The resultant cured materialexhibits an improved compression set resistance, in comparison to thefluoroelastomer cured by the bisphenol curative alone, withoutperforming a post cure procedure.

[0012] In accordance with another aspect of the invention there isprovided a curable fluoroelastomer composition comprising at least onefluoroelastomer, a bisphenol curative, and a peroxide curative, whereinwhen cured the material exhibits a higher degree of cross-linking, incomparison to fluoroelastomer cured by the bisphenol curative alone,without performing a post cure procedure.

[0013] In accordance with another aspect of the invention there isprovided a curable fluoroelastomer composition comprising at least onefluoroelastomer, a bisphenol curative, and a peroxide curative, whereinduring curing the bisphenol curative provides an initial cross-linkingand thereafter the peroxide curative deactivates the bisphenol curativeand provides a secondary cross-linking. The resultant cured materialexhibits a higher degree of cross-linking, in comparison tofluoroelastomer cured by the bisphenol curative alone, withoutperforming a post cure procedure.

[0014] While not being bound to any particular theory as to themechanism involved, it is believed that the two curative componentsprovide a two stage cure. In the initial stage, the bisphenol provides afirst level or primary cross-linking. During this stage, cross-linkingfrom the peroxide is not believed to be substantial. Near the end ofthis initial stage, the rate of cross-linking from the bisphenolcurative decreases. The second cure stage then starts. In this stage, itis believed that the peroxide cure neutralizes or deactivates thebisphenol cure and provides a secondary cross-linking reaction.Deactivation of the bisphenol curative prevents additional primarycross-linking under compression which can lead to poor compression setcharacteristics. Alternatively or, in addition, the peroxide may act inconjunction with the bisphenol and/or act as an H₂O scavenger toeliminate the ionic effects of H₂O on the fluoroelastomer polymer chain,thereby eliminating the need to perform a post cure. In any event, theprocedure provides a cured fluoroelastomer having a higher degree ofcross-linking and a markedly improved compression set resistance withoutperforming a traditional post cure step of heating (for example, heatingto about 225° C. for about 12 to 16 hours).

[0015] In accordance with a further aspect of the invention, a monomericester plasticizer is added to the curable fluoroelastomer compositionwhich comprises at least one fluoroelastomer, a bisphenol curative, anda peroxide curative. The plasticizer reduces the viscosity of thecomposition thereby facilitating molding. In addition, the resultantmolded composition exhibits improved low temperature retraction. In thisembodiment, it is preferred that the peroxide curative is in liquid formand that the plasticizer and peroxide are added together to thefluoroelastomer composition.

[0016] Through the use of the inventive curable fluoroelastomercomposition, the manufacturing process is simplified by eliminating thepost cure manufacturing step. This, of course, results in lowermanufacturing costs and reduces the manufacturing time. In addition, byeliminating the post-cure step, the manufacturing process moves furthertowards a continuous process, and away from a batch process, whichincreases efficiency and production rate.

[0017] The inventive composition is particularly useful for themanufacture of sealing elements like O-rings, flange seals and gaskets,e.g., intake manifold gaskets, rocker cover gaskets, oil pan gaskets,plastic carrier gaskets, rubber to metal bonded gaskets, and the like.The materials are especially well suited for use as gaskets that requirelow fuel permeation.

[0018] In accordance with a particular embodiment, the inventivecomposition is used to manufacture intake manifold gaskets which sealthe joint between the intake manifold and the cylinder head of theengine. Such gaskets can be manufactured separately (so-called“press-in-place” gaskets) or can be molded onto a carrier. In the lattercase, the inventive composition provides a further advantage. In priorgasket materials that required a traditional post-cure step, the carrieronto which the gasket is molded had to be constructed from materialsthat could withstand the post cure temperatures. For this reason, thecarriers used were often made form expensive heat resistant materialssuch as polyamide (PA) 6/6. However, with the materials according to theinvention, less expensive, lower heat resistant materials (e.g.,materials with a Tg (glass transition temperature) of around 200° C. orless, such as 150° C. to 200° C.) can be used for the carrier such as PA4/6 and polyether sulfone. This results in further reductions inmanufacturing costs.

[0019] The fluoroelastomers suitable for use in the disclosed inventionare elastomers that comprise one or more vinylidene fluoride units (VF₂or VdF), one or more hexafluoropropylene units (HFP), one or moretetrafluoroethylene units (TFE), one or more chlorotrifluoroethylene(CTFE) units, and/or one or more perfluoro(alkyl vinyl ether) units(PAVE) such as perfluoro(methyl vinyl ether)(PMVE), perfluoro(ethylvinyl ether)(PEVE), and perfluoro(propyl vinyl ether)(PPVE). Theseelastomers can be homopolymers or copolymers. Particularly suitable arefluoroelastomers containing vinylidene fluoride units,hexafluoropropylene units, and, optionally, tetrafluoroethylene unitsand fluoroelastomers containing vinylidene fluoride units,perfluoroalkyl perfluorovinyl ether units, and tetrafluoroethyleneunits. Especially suitable are copolymers of vinylidene fluoride andhexafluoropropylene units.

[0020] If the fluoropolymers contain vinylidene fluoride units,preferably the polymers contain up to 40 mole % VF2 units, e.g., 30-40mole %. If the fluoropolymers contain hexafluoropropylene units,preferably the polymers contain up to 70 mole % HFP units. If thefluoropolymers contain tetrafluoroethylene units, preferably thepolymers contain up to 10 mole % TFE units. When the fluoropolymerscontain chlorotrifluoroethylene preferably the polymers contain up to 10mole % CTFE units. When the fluoropolymers contain perfluoro(methylvinyl ether) units, preferably the polymers contain up to 5 mole % PMVEunits. When the fluoropolymers contain perfluoro(ethyl vinyl ether)units, preferably the polymers contain up to 5 mole % PEVE units. Whenthe fluoropolymers contain perfluoro(propyl vinyl ether) units,preferably the polymers contain up to 5 mole % PPVE units. Thefluoropolymers preferably contain 66%-70% florine.

[0021] The viscosity of the fluoropolymers can vary. Preferably, thefluoropolymers have a Mooney viscosity of 20-40.

[0022] These polymers have a certain amount of iodine and/or bromine(e.g., 0.01-5 wt %) for use with peroxide cures.

[0023] One suitable commercially available fluoroelastomer is TechnoflonFOR HS® sold by Ausimont USA. This material contains Bisphenol AF,manufactured by Halocarbon Products Corp. Another commercially availablefluoroelastomer is Viton® AL 200, by DuPont Dow, which is a terpolymerof VF2, HFP, and TFE monomers containing 67% fluorine. Another suitablecommercially available fluoroelastomer is Viton® AL 300, by DuPont Dow.A blend of the terpolymers Viton® AL 300 and Viton® AL 600 can also beused (e.g., one-third AL-600 and two-thirds AL-300).

[0024] The bisphenol curing agent provides crosslinking through basicnucleophile (nucleophilic addition) curing. The bisphenol is used inconjunction with an accelerator, such as an organophosphonium salt. See,e.g., U.S. Pat. No. 4,272,179 and “Viton Fluoroelastomer Crosslinking byBisphenols,” W. W. Schmiegel, South German Meeting of DeustcheKaustschuck Und Gummi Gesellschaft, Apr. 28-29, 1977. In nucleophilicaddition, the bisphenol curing agent forms a covalently crosslinkednetwork as a result of heating following basic dehydrofluorination.

[0025] Bisphenol curing agents that can be used in the invention arethose known within the art as being suitable for use withfluoroelastomers. See, e.g., U.S. Pat. No. 6,239,469. In general, thebisphenol crosslinking agent is used in amounts of from about 0.5-4parts by weight per hundred parts by weight fluoroelastomer (phr),preferably 1-2.5 phr.

[0026] Suitable bisphenols include those disclosed by U.S. Pat. No.6,239,469, i.e., bisphenols of the formula:

[0027] wherein

[0028] A is a stable divalent radical, such as a difunctional aliphatic,cycloaliphatic, or aromatic radical, in each case having up to 1-13carbon atoms, or a thio, oxy, carbonyl, sulfinyl, or sulfonyl radical,and A is optionally substituted with at least one chlorine or fluorineatom;

[0029] x is 0 or 1;

[0030] n is 1 or 2; and

[0031] any aromatic ring of the polyhydroxylic compound is optionallysubstituted with at least one atom of chlorine, fluorine, bromine, —CHO,or a carboxyl or acyl radical (e.g., —COR wherein R is OH, C₁₋₈-alkyl,aryl, or cycloalkyl). Combinations of two or more such bisphenolcompounds can also be used.

[0032] Suitable A groups are alkylene, alkylidene, cycloalkylene, andarylene groups, for example, methylene, ethylene, chloroethylene,fluoroethylene, difluoroethylene, 1,3-propylene, 1,2-propylene,tetramethylene, chlorotetramethylene, fluorotetramethylene,trifluorotetramethylene, 2-methyl-1,3-propylene, 2-methyl-1,2-propylene,pentamethylene, hexamethylene, ethylidene, dichloroethylidene,difluoroethylidene, propylidene, isopropylidene,trifluoroisopropylidene, hexafluoroisopropylidene, butylidene,heptachlorobutylidene, heptafluorobutylidene, pentylidene, hexylidene,1,1-cyclohexylidene, 1,4-cyclohexylene, 2-chloro-1,4-cyclohexylene,2-fluoro-1,4-cyclohexylene, 1,3-cyclohexylene, cyclopentylene,chlorocyclopentylene, fluorocyclopentylene, cycloheptylene, m-phenylene,p-phenylene, 2-chloro-1,4-phenylene, 2-fluoro-1,4-phenylene,o-phenylene, methylphenylene, dimethylphenylene, trimethylphenylene,tetramethylphenylene, 1,4-naphthylene, 3-fluoro-1,4-naphthylene,5-chloro-1,4-naphthylene, 1,5-naphthylene, and 2,6-naphthylene.

[0033] To provide for the vulcanization/curing in accordance with theinvention, the peroxides are preferably high temperature peroxides, thatis they have a slower decomposition half life. The use of such peroxidespermits the bisphenol curing reactions to proceed for a sufficientamount of time before the peroxide cure begins. This prevents theoccurrence of competing curing reaction which can result inunsatisfactory or even un-useable materials. For example, tests withvalerate peroxide and dicumyl peroxide on certainefluoroelastomer/bisphenol composition were unsuccessful (Technoflon FORHS® and is Viton® AL 200). These two peroxides have faster half lifedecompositions and start curing at around 88 to 116° C. Thus, theseperoxides may be unsuitable unless used with a bisphenol cure that has afast reaction rate. Preferably, the peroxides for use in the inventionstart curing at temperatures of about 170° C.-180° C.

[0034] The amount of peroxide cure to be used can vary and optimalamounts can be determined through routine experimentation. In general,about 0.05-5 phr (parts per hundred parts by weight of fluoroelastomer)of peroxide are used, preferably 0.1 to 3 parts by weight phr. Whiletypically only one peroxide is used, it is also possible to combine morethan one peroxide. The peroxide may be adsorbed on an inert carrier, theweight of which is not included in the above mentioned range for theamount of peroxide. In the case of Perkadox® 14/40, the amount of thisperoxide cure is preferably 1±0.3% of the total weight of thecomposition. In the case of Varox® DBPH (liquid form), the amount ofthis peroxide cure is preferably 0.75-2% of the total weight of thecomposition.

[0035] Peroxides useful as curing agents in the practice of the presentinvention include tert-butylcumyl peroxide (e.g., Trigonox® T),2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane (e.g., Trigonox® 101),alpha,alpha-bis(tert-butylperoxy-isopropyl)benzene (Perkadox® 14/40 andPerkadox® 14 (without carrier)), and2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane (Varox® DBPH-50 or Varox® DBPH(liquid form)). Another suitable peroxide is 25 Tri DYBP (with orwithout carrier).

[0036] The addition of a monomeric ester plasticizer to the curablefluoroelastomer composition can provide advantageous results withregards to viscosity and low-temperature properties. The amount ofplasticizer used is preferably 3 to 7 per 100 parts of thefluoroelastomer, especially 4 to 6 per 100 parts of the fluoroelastomer.A preferred plasticizer is pentaerythritol ester (e.g., Hercoflex 600)[Hercules, Aqualon Division]. In a preferred embodiment, pentaerythritolester is used in combination with and2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane (Varox® DBPH in liquid form).

[0037] The use of a plasticizer, for example, Hercoflex 600 incombination with Varox® DBPH in liquid form, is believed to enhance thepenetration and distribution of the peroxide into the fluoroelastomer.Preferably, the peroxide is dissolved into the plasticizer and thencombined with the fluoroelastomer.

[0038] A co-vulcanizing agent can be used in combination with theperoxide. Examples of co-vulcanizing agents include triallyl cyanurate,trimethally isocyanurate, triallyl isocyanurate (TAIC), triacrylformal,triallyl trimellitate, N,N′-m-phenylenebismaleimide, diallyl phthalate,tetrallylterephthalamide, tris(diallylamine)-s-triazine, triallylphosphate, N,N,N′,N′-tetrallyl-malonamide; trivinyl-isocyanurate;2,4,6-trivinyl-methyltrisiloxane;N,N′bisallylbicyclo-oct-7-ene-disuccini-mide (BOSA), andN,N-diallylacrylamide. Generally, the co-vulcanizing agent is used in anamount of 0.1 to 10 parts by weight per 100 parts by weight of thefluoroelastomer.

[0039] In additional to the above described components, the compositionsaccording to the invention can optionally contain additivesconventionally used in elastomeric compositions, e.g., activators,fillers, dyes/coloring agents/pigments, release agents, metal compounds,lubricants, retarding agents, thickeners, antioxidants, stabilizers,plasticizers, processing aids, etc. For example, the composition cancontain up to up to about 50% of one or more fillers, up to about 10% ofone or more activators, up to about 1.5% of one or more dyes/coloringagents/pigments, and/or up to about 0.3% of one or more release agents.

[0040] Suitable fillers include carbon black, graphite, silica, clay,diatomaceous earthy, talc, wollastonite calcium carbonate, calciumsilicate, calcium fluoride, barium sulfate, and the like. These fillerscan be used alone or in combination. Typical coloring agents includetitanium oxide, iron oxide, and the like. These can be present inamounts up to 10% by weight.

[0041] The compositions according to the invention can be prepared bycombining the components, elastomer, bisphenol curative, peroxidecurative and optional additives, for example, by Banbury mixer orpressure kneader. The resultant composition is then molded (compressionmolded, transfer injection molding, injection molding, etc.) andsubjected to heat and pressure to perform the primary curing(vulcanization), i.e., subjected to a temperature of about 175 to 200°C. and a pressure of about 10,000 to 20,000 psi for about 140 to 240minutes. As noted above, a secondary vulcanization or post-cure is notnecessary.

[0042] In the foregoing and in the following examples, all temperaturesare set forth uncorrected in degrees Celsius; and, unless otherwiseindicated, all parts and percentages are by weight.

[0043] The entire disclosure of all applications, patents andpublications, cited above and below, is hereby incorporated byreference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Various other features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood when considered in conjunction with the accompanying drawingswherein:

[0045]FIG. 1 shows the graph of time versus torque for the unmodifiedsample (Technoflon® FOR HS without peroxide) and FIG. 2 shows the timeversus torque graph for the material in accordance with the invention(Technoflon® FOR HS with the peroxide Perkadox® 14/40).

EXAMPLES Example 1

[0046] The following components are combined to form the masterbatch:Masterbatch grams 1) 66% fluorine copolymer with 100 bisphenol cureincorporated¹ 2) Magnesium oxide (activator) 9 3) Barium sulfate(filler) 65 4) Stan Tone D 4005 blue (dye) 2 5) Strutkol WS 280 (releaseaid) 0.5 176.5

[0047] To this masterbatch is added 0.6±0.2 gm of 40% activebis(t-butylperoxy-isopropyl)benzene on a clay carrier (Perkadox® 14/40,from Akzo Chemicals) to provide a total weight of 177.1 gm.

[0048] The components can be combined as follows: The FKM polymer isintroduced into a mixer and stirred for about 1 minute. Then, the filleris added and the mixture is stirred for about three minutes. Next, thedye, release aid, and peroxide are added and stirred for about a minute.The batch is removed from the mixer after a total mixing time of about 5to 6 minutes at a temperature of 230 F-235° F.

[0049] The materials were tested as follows. ASTM slabs were preparedper ASTM D2000. Compression set samples were prepared per (ISO 815/ASTMD395), and plied button compressed 25% tested 22 hours at 175° C. Theresults were as follows: the peroxide modified material in accordancewith the invention yielded 25-30% compression set, whereas theunmodified control yielded 65-70% compression set.

Example 2

[0050] The procedure of Example 1 is followed in general except that theFKM polymer used is a blend of the terpolymers Viton® AL 300 and Viton®AL 600 (one-third AL-600 and two-thirds AL-300) (manufactured byDupont-Dow) which has an incorporated bisphenol cure. The peroxide usedis 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexene (Varox® DBPH-50,manufactured by R. T. Vanderbilt Co.). In this embodiment, improvedresults are obtained when using barium sulfate as a filler (e.g., 20parts+/−5 parts per hundred parts polymer) and red iron oxide as apigment (e.g., 4 parts+/−1 parts per hundred parts polymer).

Example 3

[0051] The following components are combined to form the masterbatch:Masterbatch grams 1) 66% fluorine copolymer with 100 bisphenol cureincorporated¹ 2) Magnesium oxide (activator) 9 3) Barium sulfate(filler) 65 4) Stan Tone D 4005 blue (dye) 2 5) Strutkol WS 280 (releaseaid) 0.5 176.5

[0052] To this masterbatch is added 1±0.5 gm of liquid2,5-dimethyl-2,5-di(t-butyl-peroxy)hexene (Varox® DBPH, manufactured byR. T. Vanderbilt Co.) and added 5±1 gm of pentaerythritol ester(Hercoflex 600) to provide a total weight of 182.5 gm.

[0053] The FKM polymer is introduced into a mixer and stirred for about1 minute. Then, the filler is added and the mixture is stirred for aabout three minutes. Next, the dye, release aid, peroxide andplasticizer are added and stirred for about a minute. The batch isremoved from the mixer after a total mixing time of about 5 to 6 minutesat a temperature of 230° F.-235° F.

[0054] The material was tested for low-temperature retraction, anindication of glass transition temperature, in accordance with ASTMD1329-88, which measures the rapid evaluation of crystallization effectsand compares viscoelastic rubber materials at low temperatures.

[0055] As a result of the addition of the plasticizer, compoundviscosity was reduced from 24,670 centipoise to 1,851 centipoise. Thissignificant viscosity drop allowed the compound to be molded onto anylon 6,6 carrier (GM aftermarket 3.1L IMG). The composition releasedvery well from the mold a produced functional prototype samples.

[0056] The TR-10 (low temperature retraction) was tested in which themodification produced a significant improvement from −19° C. to −25° C.Moreover, the physical properties are more consistent due to theenhanced dispersion of the peroxide.

Example 4

[0057] The procedure of Example 3 is followed in general except that theFKM polymer used is Technoflon FOR HS® sold by Ausimont USA, i.e., a 66%fluorine fluorocarbon elastomer combined with a bisphenol curative. Theperoxide is 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexene in liquid form(Varox® DBPH, manufactured by R. T. Vanderbilt Co.) and the plasticizeris pentaerythritol ester (Hercoflex 600).

[0058] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

[0059] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A curable fluoroelastomer composition comprising at least onefluoroelastomer, at least one bisphenol curative, and at least oneperoxide curative.
 2. A curable fluoroelastomer composition according toclaim 1, wherein when cured said composition exhibits an improvedcompression set resistance, in comparison to a fluoroelastomer cured bythe bisphenol curative alone, without performing a post-cure procedure.3. A curable fluoroelastomer composition according to claim 1, whereinduring curing said bisphenol curative provides an initial cross-linkingand thereafter the peroxide curative deactivates said bisphenol curativeand provides a secondary cross-linking, the resultant cured compositionexhibiting an improved compression set resistance, in comparison to afluoroelastomer cured by said bisphenol curative alone, withoutperforming a post cure procedure.
 4. A curable fluoroelastomercomposition according to claim 1, wherein when cured said compositionexhibits a higher degree of cross-linking, in comparison tofluoroelastomer cured by said bisphenol curative alone, withoutperforming a post cure procedure.
 5. A curable fluoroelastomercomposition according to claim 1, wherein during curing said bisphenolcurative provides an initial cross-linking and thereafter the peroxidecurative deactivates the bisphenol curative and provides a secondarycross-linking, the resultant cured composition exhibiting a higherdegree of cross-linking, in comparison to fluoroelastomer cured by saidbisphenol curative alone, without performing a post cure procedure.
 6. Acurable fluoroelastomer composition comprising at least onefluoroelastomer, a bisphenol curative, a peroxide curative, and amonomeric ester plasticizer.
 7. A curable fluoroelastomer compositionaccording to claim 1, wherein said at least one fluoroelastomer is ahomopolymer or copolymer comprising one or more vinylidene fluorideunits (VF₂ or VdF), one or more hexafluoropropylene units (HFP), one ormore tetrafluoroethylene units (TFE), one or morechlorotrifluoroethylene (CTFE) units, and/or one or more perfluoro(alkylvinyl ether) units (PAVE).
 8. A curable fluoroelastomer compositionaccording to claim 7, wherein said perfluoro(alkyl vinyl ether) unitsare selected from perfluoro(methyl vinyl ether)(PMVE), perfluoro(ethylvinyl ether)(PEVE), and perfluoro(propyl vinyl ether)(PPVE) units.
 9. Acurable fluoroelastomer composition according to claim 1, wherein saidat least one fluoroelastomer contains vinylidene fluoride units,hexafluoropropylene units, and, optionally, tetrafluoroethylene units.10. A curable fluoroelastomer composition according to claim 1, whereinsaid at least one fluoroelastomer contains vinylidene fluoride units,perfluoroalkyl perfluorovinyl ether units, and tetrafluoroethyleneunits.
 11. A curable fluoroelastomer composition according to claim 1,wherein said at least one fluoroelastomer is a copolymer of vinylidenefluoride and hexafluoropropylene units.
 12. A curable fluoroelastomercomposition according to claim 7, wherein said at least onefluoroelastomer is a is a terpolymer of VF2, HFP, and TFE monomers. 13.A curable fluoroelastomer composition according to claim 12, whereinsaid at least one fluoroelastomer contains 66-70% fluorine.
 14. Acurable fluoroelastomer composition according to claim 12, wherein saidcomposition contains said bisphenol in an amount of 0.5-4 parts byweight per hundred parts by weight fluoroelastomer.
 15. A curablefluoroelastomer composition according to claim 14, wherein saidcomposition contains said bisphenol in an amount of 1-2.5 parts byweight per hundred parts by weight fluoroelastomer.
 16. A curablefluoroelastomer composition according to claim 1, wherein said bisphenolof the formula:

wherein A is a stable divalent radical, such as a difunctionalaliphatic, cycloaliphatic, or aromatic radical, in each case having upto 1-13 carbon atoms, or a thio, oxy, carbonyl, sulfinyl, or sulfonylradical, and A is optionally substituted with at least one chlorine orfluorine atom; x is 0 or 1; n is 1 or 2; and any aromatic ring of thepolyhydroxylic compound is optionally substituted with at least one atomof chlorine, fluorine, bromine, —CHO, or a carboxyl or acyl radical. 17.A curable fluoroelastomer composition according to claim 16, wherein Ais an alkylene, alkylidene, cycloalkylene, or arylene group.
 18. Acurable fluoroelastomer composition according to claim 17, wherein A ismethylene, ethylene, chloroethylene, fluoroethylene, difluoroethylene,1,3-propylene, 1,2-propylene, tetramethylene, chlorotetramethylene,fluorotetramethylene, trifluorotetramethylene, 2-methyl-1,3-propylene,2-methyl-1,2-propylene, pentamethylene, hexamethylene, ethylidene,dichloroethylidene, difluoroethylidene, propylidene, isopropylidene,trifluoroisopropylidene, hexafluoroisopropylidene, butylidene,heptachlorobutylidene, heptafluorobutylidene, pentylidene, hexylidene,1,1-cyclohexylidene, 1,4-cyclohexylene, 2-chloro-1,4-cyclohexylene,2-fluoro-1,4-cyclohexylene, 1,3-cyclohexylene, cyclopentylene,chlorocyclopentylene, fluorocyclopentylene, cycloheptylene, m-phenylene,p-phenylene, 2-chloro-1,4-phenylene, 2-fluoro-1,4-phenylene,o-phenylene, methylphenylene, dimethylphenylene, trimethylphenylene,tetramethylphenylene, 1,4-naphthylene, 3-fluoro-1,4-naphthylene,5-chloro-1,4-naphthylene, 1,5-naphthylene, or 2,6-naphthylene.
 19. Acurable fluoroelastomer composition according to claim 1, wherein saidperoxide starts curing at 170° C.-180° C.
 20. A curable fluoroelastomercomposition according to claim 1, wherein the amount of peroxide cure is0.05-5 parts per hundred parts by weight of fluoroelastomer.
 21. Acurable fluoroelastomer composition according to claim 20, wherein theamount of peroxide cure is 0.1 to 3 parts per hundred parts by weight offluoroelastomer.
 22. A curable fluoroelastomer composition according toclaim 1, wherein the peroxide is tert-butylcumyl peroxide,2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane,alpha,alpha-bis(tert-butylperoxy-isopropyl)benzene, or2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane.
 23. A curable fluoroelastomercomposition according to claim 6, wherein the amount of monomeric esterplasticizer is 3 to 7 per 100 parts of the fluoroelastomer.
 24. Acurable fluoroelastomer composition according to claim 23, wherein theamount of monomeric ester plasticizer is 4 to 6 per 100 parts of thefluoroelastomer.
 25. A curable fluoroelastomer composition according toclaim 6, wherein the monomeric ester plasticizer is pentaerythritolester.
 26. A curable fluoroelastomer composition according to claim 1,further comprising a co-vulcanizing agent selected from triallylcyanurate, trimethally isocyanurate, triallyl isocyanurate (TAIC),triacrylformal, triallyl trimellitate, N,N′-m-phenylenebismaleimide,diallyl phthalate, tetrallylterephthalamide,tris(diallylamine)-s-triazine, triallyl phosphate,N,N,N′,N′-tetrallyl-malonamide; trivinyl-isocyanurate;2,4,6-trivinyl-methyltrisiloxane;N,N′bisallylbicyclo-oct-7-ene-disuccinimide (BOSA), andN,N-diallylacrylamide.
 27. A curable fluoroelastomer compositionaccording to claim 26, wherein said co-vulcanizing agent is used in anamount of 0.1 to 10 parts by weight per 100 parts by weight of thefluoroelastomer.
 28. A curable fluoroelastomer composition according toclaim 1, further comprising one or more activators, fillers, dyes,coloring agents, pigments, release agents, metal compounds, lubricants,retarding agents, thickeners, antioxidants, stabilizers, plasticizers,processing aids, or combinations thereof.
 29. A curable fluoroelastomercomposition according to claim 28, wherein said composition contains upto up to about 50% of one or more fillers, up to about 10% of one ormore activators, up to about 1.5% of one or more dyes/coloringagents/pigments, and/or up to about 0.3% of one or more release agents.30. A curable fluoroelastomer composition comprising: at least onefluoroelastomer which is a copolymer of vinylidene fluoride andhexafluoropropylene units, a is a terpolymer of VF2, HFP, and TFEmonomers, or combination thereof, and said at least one fluoroelastomercontains 66-70% fluorine; a bisphenol curative in an amount of 0.5-4parts by weight per hundred parts by weight fluoroelastome, wherein saidbisphenol of the formula

 wherein A is methylene, ethylene, chloroethylene, fluoroethylene,difluoroethylene, 1,3-propylene, 1,2-propylene, tetramethylene,chlorotetramethylene, fluorotetramethylene, trifluorotetramethylene,2-methyl-1,3-propylene, 2-methyl-1,2-propylene, pentamethylene,hexamethylene, ethylidene, dichloroethylidene, difluoroethylidene,propylidene, isopropylidene, trifluoroisopropylidene,hexafluoroisopropylidene, butylidene, heptachlorobutylidene,heptafluorobutylidene, pentylidene, hexylidene, 1,1-cyclohexylidene,1,4-cyclohexylene, 2-chloro-1,4-cyclohexylene,2-fluoro-1,4-cyclohexylene, 1,3-cyclohexylene, cyclopentylene,chlorocyclopentylene, fluorocyclopentylene, cycloheptylene, m-phenylene,p-phenylene, 2-chloro-1,4-phenylene, 2-fluoro-1,4-phenylene,o-phenylene, methylphenylene, dimethylphenylene, trimethylphenylene,tetramethylphenylene, 1,4-naphthylene, 3-fluoro-1,4-naphthylene,5-chloro-1,4-naphthylene, 1,5-naphthylene, or 2,6-naphthylene is astable divalent radical, such as a difunctional aliphatic,cycloaliphatic, or aromatic radical, in each case having up to 1-13carbon atoms, or a thio, oxy, carbonyl, sulfinyl, or sulfonyl radical, xis 0 or 1, n is 1 or 2, and any aromatic ring of the polyhydroxyliccompound is optionally substituted with at least one atom of chlorine,fluorine, bromine, —CHO, or a carboxyl or acyl radical; a peroxidecurative in an amount of 0.05-5 parts per hundred parts by weight offluoroelastomer, wherein the peroxide curative isalpha,alpha-bis(tert-butylperoxy-isopropyl)benzene or2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane; and a monomeric esterplasticizer in an amount of 4 to 6 per 100 parts of the fluoroelastomer,and said monomeric ester plasticizer is pentaerythritol ester.